Confronting vision has emerged of a man allegedly waving a fake firearm at pedestrians on a busy Melbourne street.

The footage, obtained by 9NEWS, shows the 27-year-old strolling slowly down Chapel Street, clutching the realistic-looking firearm in his right hand yesterday.

He is seen waving the firearm at the footpath and concealing it behind his back as another pedestrian walks past.

The 27-year-old man was spotted by numerous pedestrians waving the realistic-looking firearm as he strolled down Chapel Street in Melbourne. Picture: 9NEWS (9NEWS)Frightened passers-by called Triple Zero on their mobiles. Picture: 9NEWS (9NEWS)At one point, he is seen concealing the fake gun behind his back as people walk pass. Picture: 9NEWS (9NEWS)

When police arrive, believing the weapon is real, they shout "Drop it!"

The man slowly complies, lowering his weapon to the pavement and raising his hands before police pounce, pinning him to the ground and handcuffing him.

A brave passer-by followed the man and filmed the whole scenario unfold. Picture: 9NEWS (9NEWS)Believing the gun was real, police swooped on the alleged offender. He's now been charged. Picture: 9NEWS (9NEWS)

"He just pulled back - like that. He didn't say nothing, and I thought he was going to hit me or shoot me and I've stepped back."

Another passer-by, Elliot Rothfield, said he was "absolutely" convinced the gun was real.

"I had no idea, I thought it was a real gun in his hand," he told 9NEWS.

The Prahran man was arrested for being drunk in a public place, and has now been charged over the incident.

He appeared at Melbourne Magistrates’ Court today facing charges of prohibited person possessing an imitation firearm and assault-related offences.